''Closterium'' is a

genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of living and fossil organisms as well as viruses. In the hierarchy of biological classification, genus comes above species and below family. In binomial nomencla ...

of unicellular

charophyte Charophyta () is a group of freshwater green algae, called charophytes (), sometimes treated as a division, yet also as a superdivision or an unranked clade. The terrestrial plants, the Embryophyta emerged within Charophyta, possibly from terres ...

green algae The green algae (singular: green alga) are a group consisting of the Prasinodermophyta and its unnamed sister which contains the Chlorophyta and Charophyta/Streptophyta. The land plants (Embryophytes) have emerged deep in the Charophyte alga as ...

in the family

Closteriaceae The Closteriaceae are one of four families of Charophyte green algae in the order Desmidiales (desmids).See the NCBI The National Center for Biotechnology Information (NCBI) is part of the United States National Library of Medicine (NLM), ...

.See the

NCBI The National Center for Biotechnology Information (NCBI) is part of the United States National Library of Medicine (NLM), a branch of the National Institutes of Health (NIH). It is approved and funded by the government of the United States. The ...

br>webpage on Closterium
Data extracted from the

Taxonomy

''Closterium regulare'' was first described from Lower Normandy by Brebisson.Carter, C.F. and Williamson, D.B. (2008) A rediscovered UK desmid: ''Closterium regulare'' Breb ''The Phycologist.'' Autumn 2008 No.75:24

Species

''Closterium'' includes the following species: * '' C. acerosum'' * '' C. calosporum'' ** '' C. calosporum var. himalayense'' * '' C. cornu'' * '' C. ehrenbergii'' * '' C. gracile'' * '' C. incurvum'' * '' C. littorale'' * '' C. lunula'' * '' C. moniliferum'' * '' C. navicula'' * '' C. peracerosum'' * '' C. peracerosum-strigosum-littorale complex'' * '' C. pleurodermatum'' * '' C. pusillum'' * '' C. selenastrum'' * '' C. setaceum'' * '' C. spinosporum'' * '' C. tumidum'' * '' C. venus'' * '' C. wallichii''

Reproduction

Asexual: binary fission from a partitioned parent cell. Sexual: Conjugation to form a hypnozygote. The ''Closterium peracerosum-strigosum-littorale (C. psl)'' complex is a

unicellular A unicellular organism, also known as a single-celled organism, is an organism that consists of a single cell, unlike a multicellular organism that consists of multiple cells. Organisms fall into two general categories: prokaryotic organisms and ...

isogamous Isogamy is a form of sexual reproduction that involves gametes of the same morphology (indistinguishable in shape and size), found in most unicellular eukaryotes. Because both gametes look alike, they generally cannot be classified as male or f ...

charophycean

alga Algae (; singular alga ) is an informal term for a large and diverse group of photosynthetic eukaryotic organisms. It is a polyphyletic grouping that includes species from multiple distinct clades. Included organisms range from unicellular micr ...

cells that is the closest unicellular relative to land plants. These algae are capable of forming two types of dormant

diploid Ploidy () is the number of complete sets of chromosomes in a cell, and hence the number of possible alleles for autosomal and pseudoautosomal genes. Sets of chromosomes refer to the number of maternal and paternal chromosome copies, respectiv ...

zygospore A zygospore is a diploid reproductive stage in the life cycle of many fungi and protists. Zygospores are created by the nuclear fusion of haploid cells. In fungi, zygospores are formed in zygosporangia after the fusion of specialized budding struc ...

s. Some populations form zygospores within single clones of cells (

homothallic Homothallic refers to the possession, within a single organism, of the resources to reproduce sexually; i.e., having male and female reproductive structures on the same thallus. The opposite sexual functions are performed by different cells of a si ...

), whereas others form zygospores between different clones of cells (

heterothallic Heterothallic species have sexes that reside in different individuals. The term is applied particularly to distinguish heterothallic fungi, which require two compatible partners to produce sexual spores, from homothallic ones, which are capable of ...

). The heterothallic strains have two

mating type Mating types are the microorganism equivalent to sexes in multicellular lifeforms and are thought to be the ancestor to distinct sexes. They also occur in macro-organisms such as fungi. Definition Mating types are the microorganism equivalent to ...

s, mt(-) and mt(+). When cells of opposite mating types are mixed in a nitrogen-deficient mating medium, mt(-) and mt(+) cells pair with each other and release protoplasts. This release is then followed by protoplast fusion (conjugation) leading to formation of a diploid zygospore. Sex

pheromone A pheromone () is a secreted or excreted chemical factor that triggers a social response in members of the same species. Pheromones are chemicals capable of acting like hormones outside the body of the secreting individual, to affect the behavi ...

s termed protoplast-release inducing proteins produced by mt(-) and mt(+) cells facilitate this process. A homothallic strain of Closterium forms selfing zygospores via the conjugation of two sister gametangial cells derived from one vegetative cell. Conjugation in the homothallic strain occurs mainly at low cell density and is regulated by an

ortholog Sequence homology is the biological homology between DNA, RNA, or protein sequences, defined in terms of shared ancestry in the evolutionary history of life. Two segments of DNA can have shared ancestry because of three phenomena: either a spe ...

of a heterothallic sex-specific pheromone. Although self-fertilization employs

meiosis Meiosis (; , since it is a reductional division) is a special type of cell division of germ cells in sexually-reproducing organisms that produces the gametes, such as sperm or egg cells. It involves two rounds of division that ultimately resu ...

, it produces minimal genetic variability.

Homothallism Homothallic refers to the possession, within a single organism, of the resources to reproduce sexually; i.e., having male and female reproductive structures on the same thallus. The opposite sexual functions are performed by different cells of a si ...

is thus a form of sex that is unlikely to be adaptively maintained by a benefit related to producing variability. However, homothallic meiosis may be maintained in ''Closterium peracerosum'' as an adaptation for surviving under stressful conditions such as growth in nitrogen depleted media at low cell density. A proposed adaptive benefit of meiosis is the promotion of

homologous recombination Homologous recombination is a type of genetic recombination in which genetic information is exchanged between two similar or identical molecules of double-stranded or single-stranded nucleic acids (usually DNA as in cellular organisms but may be ...

al repair of DNA damages that can be caused by a stressful environment

Fun facts

# The ends of the closterium are called polar vacuoles. # Inside the vacuoles are crystals called "gypsum crystals"

References

External links

Scientific references

Scientific databases

*
AlgaTerra database

Index Nominum Genericorum
Desmidiales Charophyta genera {{green algae-stub